Piston



Jan. 1, 1952 A. G. HERRESHOFF 2,581,326

PISTQN Filed March 29. 1949 Patented Jan. 1, 1952 UN 1 T E D "S TATES RAT ENT UFFI'CE 12,581,326 a V PIS-TON Alexander G.. Herreshoif, Grosse' 'Pointei Mich., assignor to Chrysler Corporation, :Highland Park, Mich., a-acorporationi-of' Delaware 'Applicati'onMarch 29, 1949; Serial No; 84,081

7 This invention relates to the structural design and the method of manufacture of integrally formed, composite; double-ended*pistons-adapted 11 for use in double-acting internal combustionen- 'ginesor the like.

In double acting internal combustionengines, or the like; the'cranksha'ft usually-passes transversely through the skirt portions of the doubleendedpistons, intermediate the opposed pressure heads thereof, and is connected to the pistons by means of bearing'blocks' slidably mounted in 's'lideways located interiorly of and carried by the pistonstructures.

In the pastit has-been common practice to constructpistons of this type *from two or more mating sectionsWhich are-as- Ii sembled about the crankshaft and connected together by means of tie bolts or the'likewhich'are mounted in the walls-of the' piston-"skirt portion. "A piston of the conventional, bui1t-up,= doubleended type is shown'in the application of John' P. Butte'rfield, Serial No.--16, 645, filedMarch 24,

1948. When pistons of thedouble-ended type are formed inseparable sections it is-necessary to provide relatively thick connecting wall portions 1 in the piston skirt toaccommodate the connecting meansfor the several piston sections. These relatively thickwall portions materially reduce the interior dimensions of the hollow chamber within the piston and consequently reducethe space within which the crankshaft crank arm-is adapted to rotate. -By reducing the available space within the piston allotted for thecrankshaft crank arm, the cross sectional dimension of the crank arm is accordingly'reduced-and this weakens the crankshaft and makes it less rigid and consequently subject to increased deflection.

' Deflection of the crankshafts in double actionengines causes noise and wear and has-been a source of constant trouble. This condition is 'accen tuated-in'this type of engine due to'the'fa-ctthatthe connection of the piston to the crankshaft By providing an integrally piston and thereby materially'increase the rigid-- ity of the engine assembly.

' Another objection tothe use'of-'double=ended pistons formed from built-up, separablesections isthefact that thevarious sectionsare' .frequentv *ly formed'such' that upon --assembly they are not 3 111 Claims. (Cl. 309-45) correctly aligned with their matingsections and consequently the misalignment of the various "parts has a tendency to create-binding of the 'slid'ably engaged; portions of the piston; cylinder and crankshaft and cause undue wear, noise,and

the like, during engineoperation.

'-Furthermore, to-machine the various mating piston sections and connecting means for a builtup, sectional piston is a time consuming and cost-' lyoperation. fObviously theassemblyof an engine 'usingbuilt-up, sectional, pistons is considerably more laborious and expensive than an 1 engineusing an integrally formed piston-wherein the crankshaft/can be quickly and easily threaded through the diametrically disposed openings in 'the' piston skirt and then the slideway bearing blocks assembledbetween-th e crankshaft and pis ton 'slideways.

By'forming' the double-ended piston as a compositestructure, it is possible to select certain 1 materials forthepressure. heads and different materials'-for the skirt portion and consequently the characteristics: and dimensions of the piston,

both during engine operationand at other times,

maybe very closely controlled. Inthe composite piston-herein" disclosed a lightweight material of good ithermal' conductivity that has. a' relatively :high 'coefiici'entj of expansionwithin the normal engine temperature range and iscapable of being easily die cast or machined'is-prefe'rably selected -for the pressureaheads. Aluminum and alloys thereof have provenxto be: particularly advantageous for forming. the piston pressure heads. The particular advantagesofrsuch amaterial for the pressure heads are more fullysexplainedhereafter. The-skirt portion of this composite piston is-preferably formed .from'a relatively stiff material that is a relatively'poor thermal'conductor 5' and one that ;has.a relatively, low coeflicient of 'expansionwhen subjected to heat. Such a ma terial should beqcapable of being cast, extruded,

rolled and-welded. :Steel and the alloys thereof 'have proven suitable for-use as a skirt portion material. The advantages of such a material for the skirt'portion of this piston are also more fully set forth subsequently.

It is aprimary obj ectof this invention torprovide a unitary, composite; double-endedpiston designed and constructed in such amannerithat it is extremely efiicient'in operation and simple '-andeconomical to manufacture and assemble. v

Itfis afurther' object of this invention to provideaunitary; composite double-ended piston I which has a'ininimum*skirt wallfthickness1so as *t0 permit the use'pf a crankshaft of-maximum a composite, unitary, double-ended piston of the type having bearing block slideways supported interiorly thereof wherein the slideways are formed as parts of the pressure heads and disconnected from the piston skirt so as to render the slideways more flexible to thermal expansion and at the same time provide a relatively cool piston skirt that is adapted to be arranged in a cylinder bore with minimum clearance therebetween.

It is a further object of this invention to pro vide a unitary, composite, double-ended piston formed from relatively simple elements connected together in a simple and novel manner.

Fig. 1 is a side elevation with portions broken away and partly in section, of a unitary, doubleended, internal slideway type of composite piston embodying this invention;

Fig. 2 is a sectional elevation of the piston shown in Fig. 1, the view being taken along the line 2-2 of Fig. 1;

Fig. 3 is an enlarged, fragmentary, sectional elevation of that portion of the piston within the circle identified by the numeral 3 in Fig. 1; and

Fig. 4 is a fragmentary sectional elevation of a modification of the skirt and head connection shown in Fig. 3.

In a double-acting type of internal combustion engine a double ended or double-headed type of piston is employed for reciprocatory movement in each cylinder bore, the engine being designed to provide a combustion chamber at each end of each cylinder to cooperate with each end or head of each piston. Engines of this type employ a crankshaft which threads through the skirt portions of the pistons and is directly connected to the pistons without the use of a conventional connecting rod. The connection of the crankshaft to the pistons is by means of bearing blocks journaled on the crankshaft crank pins and slidably engaged with a pair of slideways carried by and supported interiorly of each piston.

A few of the difficulties encountered with engines of this type have been the lack of rigidity in the crankshafts and the inability to maintain sufficiently close clearances between the piston slidea ways and the crankshaft bearing blocks, and between the pistons and cylinder bores during engine operation so as to keep engine wear, noise and power loss to a minimum. It has been found that with conventional double-headed pistons the combustion heat from the two opposed piston heads is readily transmitted to the piston skirt and to the interior slideways during engine operation and these portions of the piston expand and tend to enlarge the clearances between the bearing block and the slideways with the result that the combustion heat will ordinarily cause the skirt to expand more than the struts supporting the slideways therefore its is obvious that the clearances between the crankshaft bearing block and slideways will be opened up during engine operation. Furthermore, if the oppositely disposed ends of the slideways are connected to the piston skirt then any inward axial expansion, longitudinally of the piston, by the slideways, is retarded by the connection of the slideways to the skirt and the situation is even more aggravated for the ends of the slideways are bent towards the piston heads by the heat of combustion and this opens up the slideways. By providing a construction wherein the slideways are disconnected from the skirt portion the skirt runs cooler than would otherwise be the case and the clearances between the piston and surrounding cylinder bore may be set closer and the efiiciency of the engine unit improved. This invention overcomes the aforementioned difficulties and provides an improved, low cost, double-ended piston construction that lends itself to accurate control of the piston clearances and at the same time provides a piston that permits use of a stiffer crankshaft to counteract undesirable deflections and vibrations of the crankshaft during engine operation.

The letter A represents a double-ended piston structure having a substantially cylindrical head portion 12 at each end thereof and a slotted, substantially cylindrically shaped, sleeve-like skirt portion I4 extending between and connecting the spaced head portions i2. Each head portion I2 along its peripheral edge is formed with a depending flange portion 13 having a spaced set of circumferentially extending piston ring grooves I6. Extending about the skirt portion 14, adjacent each set of piston ring grooves I5, is a set of grooves ll adapted to trap oil and provide a series of oil wedges between the piston skirt and the surrounding bore of the engine cylinder in which the piston structure A is mounted.

The piston structure A also has its skirt portion l4 formed with diametrically disposed pairs of axially extending slots 22 and 24 respectively. The

slots 22 are displaced circumferentially ninety degrees from the slots 24. Slots 22 are adapted to receive the crankshaft (not shown) which is the piston structure A on the slideways 32. Posiversely of the longitudinal axis of the piston structure A and is supported from the associated piston head 12 by means of the crossed struts 38 and 38 respectively. Struts 36 are of variable depth and sweep radially outwardly from the slideway 32 towards the associated piston head l2 whereas struts 38 are of full depth throughout the length of the slideivay 32 as clearly indicated at 39 of Fig. 1. By this arrangement the heat of the piston head l2 may be readily transferred to the slideway 32 by the struts 36 and 38. It

iscpreferable thaa.. the:-piston head. I25 andthe; slidewayesupportihgsstruts:35; 38 be: formed from materia'h such: as: aluminum having as; relatively.- highzcoefiicient?ofiexpansioniwithin.. the :temp era:

turecrange: "oft. tires-combustion chamber: of the: conventional; internalscombustion; enginerso that; the. toll benefits: oilthermal; expansion... of the. strut'szmay be utilized: It-will-be noted; that the ends'33': of the: slidewayportions 32 extend into the; diametrically disposed-1 slots; 2l in the-pistons, skirt I4 but are disconnected from the adjacent skirt? portiom This: arrangement oh the; struts and 'slideways prevents transfer of heat' fromthe slideways-M-to theskirt portion ld andrtendsrtokeep the? skirt portionirelatively cool during engine operation. The: pistomskirt: portion I14: is.- preferably formed fromsteel orsome alloy-thereof which "is relatively strong .andastiff and has-a: coeificient of. expansion'wthat is considerably less .1 than that of the :materialusedfor. the-pressure heads -I 2-. By-having-the Fends of the slidewa-ys 32 disconnected. from the piston skirt portion .Idthe:- slideways=are :rendered more fiexible and. are free to thermally; expandaxially of: the. pistontowards the: crankshaft bearing. block, which is mounted betweenthe slideways.-- The relatively. largev thermal expansionof; the 'slideway struts during engine operation, duetocombustion-heat;

and: the relatively small piston'skirtexpansion,

resulting from the difierences incoefficients .of

exhaustion. and thermaleconductivity ofthe materials used for the piston heads and skirt. portion, tends to. reduceto. ai-min-imum duringengine operation. theclearances betweenthe slidably en-- gaged, crankshaft. bearing; block andithe piston. slidewaysv 32 and thus. provides a.- smoothly oper-. ating,. relatively noiseless. engines While; the. thermal expansion oi the slideway, struts 36, 33 reduces the: clearancesbetween the. crankshaft. bearin-giblock andrthe=slideways 32 during engine operation, it is obvious thatthermal contraction: will open .up :these clearancesa-nd preventseizure of.these.elements when the engineis cold-or dura ing enginestart...

Theexposed .slide faces. 34 of the slideW-ays- 32 are preferably cylindricalsections.- that. provide arcuate. bearing surfaces facing.v eaclr other and spaced. apart. a distance. slightly greatenthanthe efiective. width oiudiametenof the mating. bearing. block 1 (not shown). thatisjournaled on .the. asso ciated. crankshaft (notshown) and slidably associated with. the pistonislideways 32.. The axislof the curved bearing faces 34' of slideways. 32'- istransversely ofn and. normal to. the. longitudinal axis. of .the pistonstructure A- Thepiston skirtportion-l4lis connected torthe. spaced pressure heads. I 2.. by meansof a. sweated or shrunk connection, see Fig, 3,7that takeslad vantageof' the. physical properties -of.lthe. ma.' terials from \vhich.the pistonheads and sld-rtare formed; The. interior surfaceof; each-end ofithe cylindrical piston skirt. L4 .is .formedlwithaseries. of radially extending. inwardly, directed}. projece. tions I 5; the. projections resembling teeth, .serrae. tions,'screw threadsor thelike- Thenormal..ont.-. side diameter of the fi'ange. portions. I.3..of;'the. piston heads I! is. slightly. greater than the. nor.- mal interior diameter of the. cylindricalpiston skirt I4. Toassemble the .piston heads I2, on the skirt .portion E4 the skirt portion Mis. heated.- to an abnormally high temperature and. the. pistonheads. are usually cooled to anabnormally low temperaturewhereupon diametrical expan=- sion. of the piston skirtandcontraction. of the. piston heads Will permit. these elements. to. .be

assembled in telescopic relationship. As the skirt 75.

pcntion. iscsubsequentlycooledato its normal terrrei perature:theiprojections I.5: th'ereon bite: into-ether pistonihea-d flanges; I 31andnlocking-ly connect-the heads -I2.-to the skirt portionaI I. As the headsll are warmed.-to-theinnormal temperaturethey tendto. expand and press outwardly. against the. teeth-likeprojections. l 5;. Itlisv obvious -that both. mating .elements I2 and. [4 may have-their.temperatures varied .to cheat the shrunk connection describedor either one of these. elements may be.

treated to vary'its expansion. and/or contraction so' as to accomplish the shrunk connection; In place of the shrunk connection a conventional screw" thread connection could be used" but such' would be: considerably more expensive to manufacture and assemble than the shrunk connection herein proposed. The-shrunk connection also takesfadvantage? ofthe physical' properties" of the materials from: which .the heads' I z an'd skirt I4 are? formed forthesteelv teeth I5 on: the skirt: I4 are sufli'ciently hard toiibit'e into the relativel'ysoft 1 sides ofith'e flanges: I'3Toftthe aluminum heads: I12.

modifiedv form 1 of." connection between" the: piston? heads" I2 and'. piston skirtxporti'on- I4 is ShOWniin'. Fig: 4';.'In1this-form?ofthe invention a, fused and/ore; bolted orrivetedf'connecti'on. be'-- tween the pistorrv head. flange I3 and the sur-- rounding piston skirt :portion I4 is disclosed; A ring: element. 51" of steel orxth'e' like is. shrunk on the head fi'ange-portion f3 "an'd'anchored thereto by means of the projections-'52 which are similar to the projections I5 shown in Fig. 3; Theskirt portion M is then connected-Ito the'ringeleme'nt through the skirt portion I4, ring 5| and head flange =43 to more positivelyassociate these elements.-

It is' thought to be obvious that the unitary,

composite; double en'ded interna-lsliding'type of piston herein disclosed is easy and economically r fabricated and assembled and at the same time isdesigned'so-as to provide apiston unit. that is highly efiicient in operation due to the piston structure permitting accurate control of all" working" clearances; Theopposed pressure heads;

IZ are identical andican' be simple castings .that includethe bearing; block slideways 32.

canbe extruded", cast'or 'rolled and subsequently machinedto fin'e dimensionsif necessary; Y'I'he, assemblyofthe' elements .of this piston is a'novel" and relatively simple process that lends" itself" to current, mass production practices. When assembled; in finall'form thispiston unit may be quioklyand easily mounted on. a unitary crank-.

shazft unit and connected thereto by bearing block means such .as that shownv in. the. applicaticn. ofIIArthur. .vl slemmons Serial. No" 80,729,,

and a..hol1ow substantially, cylindrical. skirt ofsteel or the likeconnecting .said.heads, the. means connecting... said skirt and said;..-heads ix-ic ludingi;

The. skirtportionis a simple sleeve element that.

end portions on said skirt arranged to extend concentrically about said heads in contiguous relationship thereto and radially projecting serrations along the skirt end inner surfaces contacting said heads and thermally shrunk into engagement with the adjacent exterior surfaces of said heads so as to embed the skirt serrations in said heads, said heads each including an axially projecting bearing block slideway supported from the interiorly arranged end of the head and positioned to extend transversely of the skirt between opposite sides thereof but to be disconnected therefrom, said slideways being axially spaced apart and adapted to reciprocably receive a bearing block mounted therebetween.

2. A composite double-ended piston comprising a pair of opposed, axially spaced, substantially cylindrically shaped heads formed of a material having a high coefficient of expansion and being of low density, and a hollow, relatively thin walled, substantially cylindrical skirt connecting said heads formed of a material having a low coeflicient of expansion and a high modulus of elasticity, said heads each including an axially projecting bearing block slideway supported from the interior end of the head and arranged to extend transversely of the skirt between opposite sides thereof but disconnected therefrom, said slideways being axially spaced apart and adapted to reciprocably receive a bearing block mounted therebetween.

3.- A composite double-ended piston comprising a pair of axially spaced, opposed, substantially cylindrically shaped heads formed of aluminum or a material having similar physical properties relating to thermal expansion and contraction, stiffness and wear resistance, and a hollow substantially cylindrical skirt connectingsaid heads formed of steel or a material having similar physical properties relating to thermal expansion and contraction, stiffness and wear resistance, said heads each having a depending bearing block slideway extending from the interior end thereof and arranged with the slide face thereof extending transversely of the piston skirt between opposite sides thereof but disconnected therefrom, said slideways being axially spaced apart and adapted to reciprocably receive a bearing block mounted therebetween.

4. A unitary, double-ended, composite piston comprising a pair of axially spaced, opposed, substantially cylindrically shaped, piston heads each having a depending, axially extending peripheral flange portion and an axially projecting, transversely extending slideway depending from the inner opposed end surface of each head and extending between diametrically disposed portions of the piston, said slideways being axially spaced to receive a reciprooably mounted bearing block, and a hollow cylindrically shaped, axially slotted, skirt member arranged concentrically about and connected to the flange portions of said piston heads, said skirt portion encircling but being disconnected from the slideways on said piston heads.

' 5. A unitary, composite double-ended, internal slideway type of piston comprising a pair of spaced, axially aligned, substantially cylindrically shaped, piston heads, formed from a ma-- terial having a relatively high thermal conductivity and coeiiicient of expansion, said heads each having a transversely extending, axially projecting slideway supported from the opposed inner end of each head and extending between diametrically disposed portions of the supporting head, and a hollow cylindrically shaped skirt member. having axially extending slots therethrough and radially extending, inwardly projecting protuberances formed on the skirt inner walls adjacent each end thereof adapted to be fixedly engaged with encircled portions of the outer walls of the piston heads, said skirt member being formed from material having a relatively low coefiicient of expansion and being arranged so as to encircle but be out of contact with said slideways.

6. A unitary, composite, double-ended internal slideway type of piston comprising a pair of axially spaced, axially aligned, substantially cylindrically shaped, piston heads, formed from a material having a relatively high thermal conductivity and coeflicient of expansion, said heads each having a transversely extending, axially projecting bearing block slideway supported from the opposed inner end of each head and extending between diametrically disposed portions of the head, and a substantially hollow cylindrically shaped skirt member having axially extending slots therethrough and radially extending, projecting formations on the inner skirt side wall adjacent each end thereof adapted to be fixedly engaged with concentrically arranged portions of the side walls of the piston heads, said skirt memher being formed-from material having a relatively low c-oefiicient of expansion and being arranged so as to encircle but be out of contact with said slideways.

7. A unitary, composite, double-ended, internal slideway type of piston comprising a pair of axially spaced, axially aligned, substantially cylindrically shaped, piston heads, formed from a material having a relatively high thermal conductivity and coeflicient of expansion, said heads each having a transversely extending, axially projecting bearing block slideway supported from the opposed end of each head and extending between diametrically disposed portions of the head, a ring-like member mounted on each head so as to extend concentrically about a side portion of each head, and a hollow, substantially cylindrically shaped skirt member having axially extending slots therethrough and the ends thereof connected to and extending concentrically about the ring-like members, said skirt member being formed from material having a relatively low coefficient of expansion and being arranged so as to encircle but be out of contact with said slideways.

8. A unitary, composite, double-ended, internal slideway type of piston comprising a pair of axially spaced, axially aligned, substantially cylindrically shaped, piston heads, formed from a material having a relatively high thermal conductivity and coefiicient of expansion, said heads each having an axially extending peripheral flange portion and a transversely extending, axially projecting bearing block slideway supported from the opposed inner end of each head and extending between diametrically disposed portions of the head, said slideways each having a bearing surface curved about an axis extending transversely of and normal to the piston axis, and a hollow, substantially cylindrically shaped skirt member having axially extending slots therethrough and radially extending, inwardly projecting protuberances formed on the inner skirt wall adjacent each end thereof adapted to be engaged with the concentrically disposed walls of .the flanges on the piston heads, said skirt member being formed from a material having a relatively low coefficient of expansion and being arranged so as to encircle but be out of contact with said slideways.

9. A double-ended piston comprising a pair of axially aligned and axially spaced, substantially cylindrically shaped, head portions connected together by a concentrically arranged, hollow, substantially cylindrically shaped skirt portion, said head portions each having a bearing block slideway projecting from the inner side of the head portion arranged to extend transversely of the piston skirt portion between diametrically disposed portions thereof but disconnected therefrom, the bearing surfaces of said slideways being axially spaced apart and aligned to reciprocably receive therebetween a bearing block.

10. A double-ended piston comprising 'a pair of axially aligned and axially spaced, substantially cylindrically shaped, head portions connected together by a concentrically arranged, hollow, substantially cylindrically shaped skirt portion, said head portions each having a bearing block slideway projecting from the inner side of the head portion arranged to extend transversely of the piston skirt portion between diametrically disposed portions thereof but disconnected therefrom, the bearing surfaces of said slideways being axially spaced apart and aligned to reciprocably receive therebetween a bearing block, and said hollow skirt portion having axially extending slots therethrough disposed at substantially right angles to the direction of the slideways adapted to receive a crank member.

11. A double-ended piston comprising a pair of axially aligned and axially spaced, substantially cylindrically shaped, head portions connected together by a concentrically arranged, hollow, substantially cylindrically shaped skirt portion, said head portions each having a bearing block slideway projecting from the inner side of the head portion arranged to extend transversely of the piston skirt portion between diametrically disposed portions thereof but disconnected therefrom, the bearing surfaces of said slideways being axially spaced apart and aligned to reciprocably receive therebetween a bearing block, and said hollow skirt portion having axially extending slots therethrough disposed at substantially right angles to the direction of the slideways adapted to receive a crank member, said hollow skirt portion having other axially extending slots therethrough displaced substantially ninety degrees from said first mentioned slots and aligned with said slideways.

ALEXANDER G. I-IERRESHOFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 706,711 Andres Aug. 12, 1902 750,565 Austin Jan. 26, 1904 1,254,353 a Priest Jan. 22, 1918 1,357,851 Diamond Nov. 2, 1920 1,427,673 Allen Aug. 29, 1922 1,427,930 Baker Sept. 5, 1922 1,721,197 Almen July 16, 1929 1,933,749 Murray Nov. 7, 1933 1,978,045 Flower Oct. 23, 1934 2,174,218 Greene Sept. 26, 1939 2,267,339 Paulsen Dec. 23, 1941 2,270,278 Dunn Jan. 20, 1942 

